Double action pressure switch



y 1966 L. c. FRIEND ETAL 3,251,959

DOUBLE ACTION PRESSURE SWITCH Filed Aug. 1. 1961 2 Sheets-Sheet 1 i 46 f /75 4 :14 /44 f /50 172 1 I I I. r 66-- 42 /Z 54- .5 1! 45 IN VEN TOR. man/79th D. S/za ub BY L/hdsa Y C. Fh/vd May 17, 1966 I... c. FRIEND ETAL 3,251,959

DOUBLE ACTION PRESSURE SWITCH Filed Aug. 1. 1961 2 Sheets-Sheet z Z; /74 20 494 79' /j5vZ Z4 z: I y

* 775.5 776. 4 INVENTORS United States Patent 3,251,959 DOUBLE ACTION PRESSURE SWITCH Lindsay C. Friend, Lutherville, and Kenneth D. Shaub, Timonium, Md., assignors to The Bendix Corporation, Towson, Md, a corporation of Delaware Filed Aug. 1, 1961, Ser. No. 128,551 6 Claims. (Cl. 200-83) .This invention relates to pressure actuated switching devices and more particularly to a pressure switch having especial utility for use with rockets and missiles or other applications imposing severe environmental conditions.

With the advancing technology related to rockets and extreme high altitude flight,-it has become necessary to provide sensing devices capable of providing higher and higher degrees of sensitivity for measuring the small pressure variations encountered and at the same time capable of resisting severe environmental conditions of heat, vibration,' shock and G loads. Not only can such conditions actually damage or destroy the pressure switches, but they are most likely to render them inaccurate Efforts to make the switches more rugged mechanically have often resulted in reducing their sensitivity as well as increasing their size and weight. It has often been found that an otherwise satisfactory pressure switch has been I prone to chatter at comparatively low vibration frequencies because the contacts respond to harmonics of the resonant frequency of the system. This normally requires isolating devices such as rubber pads or grommets to be used. It is therefore an object of the present invention to provide a pressure-responsive switching device having a high degree of sensitivity but which is extremely rugged and resistant to extreme environmental conditions of shock and G loads.

It is another object of the present invention to provide a pressure-responsive switching device which accomplishes the above object but which can be made in an extremely small and light package.

It is another object of the present invention to provide a pressure sensitive switching device which accomplishes the above objects and which has a high degree of repeatability, i.e., ability to give the same response consistently within a very small margin or error.

It is another object of the present invention to provide a pressure-responsive switching device which accomplishes the above objects and in which the electrical contacts are not subjected to the humidity conditions of the pressure sensitive element thereof enabling the device to retain its original electrical performance during extended periods of operation 'in humid environmental conditions. Q

It is a further object of the present invention to provide a pressure-responsive switching device in which auxiliary isolating device's are not required to maintain a high degree of resistance to chatter of the contacts.

Other objects and advantages will become apparent from consideration of the following specification taken in connection with the accompanying drawings in which:

FIG. 1 is a sectional view of our switching device taken on line 11 of FIG. 2;

FIG. 2 is a sectional view taken on line 2 -2 of FIG. 1

but with the pressure-responsive diaphragm member in-.

with the pressure-responsive diaphragm member and the entire housing included; and

FIG. 5 is a sectional view taken on line 5-5 of FIG. 1 with the pressure-responsive diaphragm member included.

Referring now to FIG. 1, which is drawn to approximately four times the scale of the device as built, the switching structure is mounted on a base plate 10 which supports a plurality of columns or posts 12 which carry a circular flange member 14 (see FIGS. 2-5). Flange member 14 includes an axially projecting flange 16 (see FIG. 4) which contains a radially extending flange 18 of the circular diaphragm member 20. A retaining ring 22 abuts against the inside of flange 16 and against flange 18 and members 14, 18 and 22 are welded together. A cover 24, Welded to a radially extending flange 26 of member 14, cooperates with diaphragm 20 to form a chamber 28. A conduit30 provides communication between chamber 28 and the source of pressure to be sensed.

Attached to the center of diaphragm 20 is a push rod 32 which is actually in the form of a comparatively thin, wide plate. This push rod has its opposite end fastened to two ceramic insulating blocks 34 and 36 which are, in turn, attached to two levers 38 and 40, respectively. Lever 38 carries a switch contact 42 and a counterweight 44 and is arranged to pivot around the apex of a triangular flexure support member 46. Lever is attached to the opposite side of push rod 32 from lever 38 and carries a switch contact 48 and a counterweight 50 and pivots around the apex of a triangular flexure support member insulating pads 47 and 53, respectively, on the base 10 and allow levers 38 and 40 to pivot by bending one leg convexiy while the other leg is bent concavely yet the flexure members are rigid in all three planes.

Switch contact 42 on lever arm 38- makes contact with a switch contact 54 as the pressure in chamber 28 is reduced below a threshold value and the contact 48 on lever arm 40 makes contact with a switch contact 56 as the pressure in chamber 28 is increased above a threshold value. Aspacer member 60 supports contact 54 and these members are carried by an arm 62 which is part of a resilient support member 64 which urges arm 62 in a direction tending to move contact 54 against contact 42. The resilient force of member 64 is opposed by a pair of inter-connected threaded members 66 and 68 which provide a means of adjusting the position of contact 54 and, hence, the sensitivity of this switch element, externally of the unit. A bellows 70 provides a means for permitting this adjustment while maintaining a seal across plate 10.

As the pressure in chamber 28 increases, it causes arm 40 to be rotated counterclockwise (as seen in FIG. 3) around the apex of flexure 52 and contact 48 is urged against contact 56 which is carried on a leaf spring member 72. The leaf spring member 72 has a spring rate which is appreciably lower than that of flexure 52 so that flexure 52 is not permanently deformed when the diaphragm 20 is moved over an extreme range. In order to insure the repeatability of these contacts, when the arm 40 is rotated clockwise (see FIG. 3) and the contact 56 is tending to follow contact 48, the contact 56 is caused to abut against a contact 73 attached to a spacer 74 (see FIG. 5), both of which are carried on an arm or support member 75, thus permitting contact 48 to move away from contact 56. Support member 75 is attached to a flexure member 76 which is movable by means of an arm 77 which passes through a seal including a bellows 78 in base plate 16. By adjusting the position of arm 77 and, hence, the support member 75, an adjustment of the switch constituted by contacts 48 and 56 may be made.

The electrical connections through this pressure-responsive switching device, as shown, require that the base plate be grounded and that sealed passages be provided therethrough to admit a pair of contactors energized at Attached to the base of flexure members 46 and 52 are electrical terminals 92and 94, respectively. A wire 96 connects terminal 86 to terminal 92and a wire 98 connects terminal 90 to terminal 94. If terminals 86 and 90 are assumed to be positive, with respect to ground, an increasing pressure acting against diaphragm 20 causing lever 40 to be moved in a counterclockwise direction will close switch member 48 against member 56, thus causing current to flow from terminal 90 through wire 98 to terminal 94, through flexure 52, lever arm 40 and contact 48, contact 56 to leaf spring 12 to support member 75 which is efifectively attached to the grounded base plate 10, thus energizing any external circuit connected to terminal 90. A decreasing pressure acting against diaphragm 20 causing lever 38 to be moved in a counterclockwise direction closing contact 42 against contact 54 will cause current to flow from terminal 86 through wire 96 to terminal 92, through flexure 46, lever 38, contacts 42 and 54, spacer 60, arm 62, and support member 64 which is grounded on base plate 10. Obviously both sides of the switching contacts could be at other than ground potential if stationary contacts 54 and 56 were insulated from the housing, but an additional sealed conductor must be passed through the base plate 10 or the wall of the vessel for each pair of contacts.

The pressure-responsive device described herein thus provides one set of contacts which close on increasing pressure and one set which close on decreasing pressure. The counterweights 44 and 50 act to compensate for the mass of the diaphragm 20 and associated structure such that the device is mass balanced and inherently stable under extreme vibration and acceleration conditions. This design effectively removes weight or loading from the diaphragm. Inasmuch as such loading tends to lower the effective resonant frequency of the system in proportion thereto, it reduces the vibration range over which the system will operate withoutchattering of the contacts or the requirement for adding isolating devices to minimize such chatter. With the present device it has been found that the natural frequency of the effectively unloaded ing devices have not been required. A further advantage of the design shown herein is that the diaphragm may be made so stiff (thus raising the resonant frequency) that diaphragm motion alone would not satisfactorily operate the contacts, but with the lever multiplication factor of the balance arms, the small motion of the diaphragm will provide enough travel for satisfactory switching.

While only one embodiment has been shown and described herein, modifications may be made without departing from the scope of the present invention.

What we claim is:

1. In a pressure-responsive switching device including a housing, a diaphragm in said housing dividing said housing into a pressure-sensing chamber and a sealed chamber, a passage communicating said sensing chamber with a source of variable pressure, a push rod in said sealed chamber attached to said diaphragm, a base plate froming part of said sealed chamber including electrical insulating means attached to the surface thereof, a pair diaphragm is at a sufficiently high value that such isolatof levers attached to said push rod each of which carries a switch contact, a pair of fiexure members mounted on said insulating means and providing fulcrums for each of said levers, electrical insulating means positioned between said push rod and said levers, a counterweight positioned on each of said levers on the opposite side of said fulcrums from said push rod, a first resiliently mounted contact coacting with one of said switch contacts, a second resiliently mounted contact coacting with the other of said switching contacts, means for varying the effective clearance between said contacts and said-switch contacts, and a conductor adapted to carry an electric-a1 current connected to at least one of each pair of coacting cont-acts.

2. A pressure-sensing device as set forth in claim 1 wherein at least one of said means for varying the clearance between said contacts includes a flexure member attached to said base plate and said resiliently mounted contact, an armextending externally of said housing attached to the movable part of said flexure member, and a bellows providing a seal around said arm across said base plate.

3. In a pressure-responsive switching device including a housing, a diaphragm in said housing dividing said housing into a pressure-sensing chamber and a sealed chamber, a passage communicating said sensing chamber with a source of variable pressure, a push rod in said sealed chamber attached to said diaphragm, a base plate forming part of said other chamber including electrical insulating means attached to the surface thereof, a pair of levers attached to said push rod, each of said levers including a switch contact, a pair of flexure members mounted on said insulating means and providing fulcrums for each of. said levers, electrical insulating means positioned between said push rod and said levers, a counterweight positioned on each of said levers between said fulcrums and said switch contacts, a first stationary contact for coacting with one of said switch contacts including resilient mounting means effectively fastened to said housing, a second stationary contact adapted to prevent said resiliently mounted contact from following said one switch contact as said one switch contact is moved away from said resiliently mounted contact, a third stationary contact adapted to coact with the other of said switch contacts, resilient mounting means for said third contact effectively fastened to said housing, means connected to said resilient mounting means for adjusting the switch constituted by said other switch contact and said third stationary contact, and a conductor adapted to carry an electric current connected to at least one of each pair of coacting contacts.

4. In 'a pressure-responsive switching device including a housing, a diaphragm in said housing dividing said housing into two chambers, a passage communicating one of said chambers with a source of variable pressure, a push rod in the other of said chambers attached to said diaphragm, a base plate forming part of said other chamber, lever means attached to said push rod including a switch contact, supporting means for said lever means comprising a triangular flexure member mounted on said base plate which is substantially rigid in all three dimensions yet sufiiciently flexible to permit said lever means to pivot around the apex of said flexure member, counterweight means positioned on said lever means on the opposite side of said fulcrum from said push rod, a contact co-- operating with said first-named switch contact, and a conductor adapted to carry an electric current connected to one of said contacts.

5. A pressure-responsive switching device as set forth in claim 4 wherein means are provided for varying the clearance between said contacts comprising a resilient supporting device for said contact including a fiexure member fastened to said housing, an arm extending externally of said housing attached to the movable part of said fiexure member, and bellows means providing a flexible seal around said arm through the Wall of said housing.

6. A switching device comprising a pressure-responsive device, a push rod attached to said pressure-responsive device and responsive to movements thereof, a lever attached to said push rod including a switch contact, a base plate in spaced relationship to said lever and supporting means for said lever comprising a triangular flexure mem- References Cited by the Examiner UNITED STATES PATENTS Schulte 200-83 Newton 200-83 Welch 200-83 Wallace ZOO-83 Murphy 200-83 Hamburg 200-83 10 BERNARD A. GILHEANY, Primary Examiner.

s. B. SMITH, JR., H. M. FLECK, 1a.,

Assistant Examiners. 

1. IN A PRESSURE-RESPONSIVE SWITCHING DEVICE INCLUDING A HOUSING, A DIAPHRAGM IN SAID HOUSING DIVIDING SAID HOUSING INTO A PRESSURE-SENSING CHAMBER AND A SEALED CHAMBER, A PASSAGE COMMUNICATING SAID SENSING CHAMBER WITH A SOURCE OF VARIABLE PRESSURE, A PUSH ROD IN SAID SEALED CHAMBER ATTACHED TO SAID DIAPHRAGM, A BASE PLATE FROMING PART OF SAID SEALED CHAMBER INCLUDING ELECTRICAL INSULATING MEANS ATTACHED TO THE SURFACE THEREOF, A PAIR OF LEVERS ATTACHED TO SAID PUSH ROD EACH OF WHICH CARRIES A SWITCH CONTACT, A PAIR OF FLEXURE MEMBERS MOUNTED ON SAID INSULATING MEANS AND PROVIDING FULCRUMS FOR EACH OF SAID LEVERS, ELECTRICAL INSULATING MEANS POSITIONED BETWEEN SAID PUSH ROD AND SAID LEVERS, A COUNTERWEIGHT POSITIONED ON EACH OF SAID LEVERS ON THE OPPOSITE SIDE OF SAID FULCRUMS FROM SAID PUSH ROD, A FIRST RESILIENTLY MOUNTED CONTACT COACTING WITH ONE OF SAID SWITCH CONTACTS, A SECOND RESILIENTLY MOUNTED CONTACT COACTING WITH THE OTHER OF SAID SWITCHING CONTACTS, MEANS FOR VARYING THE EFFECTIVE CLEARANCE BETWEEN SAID CONTACTS AND SAID SWITCH CONTACTS, AND A CONDUCTOR ADAPTED TO CARRY AN ELECTRICAL CURRENT CONNECTED TO AT LEAST ONE OF EACH PAIR OF COACTING CONTACTS. 